The present invention relates to accommodation of the eye and treatment of presbyopia.
The eye has a cornea and a lens. The cornea and lens focus light on a retina such that the person can perceive the image with the retina located on the back of the eye. When the image on the retina is focused, the image appears sharp to the patient. However, when the image is out of focus, the image appears blurred. An eyeglass prescription to correct far vision of the eye can be referred to clinically as a refraction of the eye, and the measured refraction of the eye can include a sphere, a cylinder and an axis of the cylinder. Corrective lenses can be prescribed based on the refraction of the eye such that optical errors of the eye such as nearsightedness, also referred to as myopia, and farsightedness, also referred to as hyperopia, can be corrected. Nearsightedness corresponds to an eye having too much optical power such that objects near the eye appear in focus and distant objects appear blurred. With a nearsighted eye, lenses having negative optical power can be used to correct the refractive error of the eye. Farsightedness can refer to an eye not having enough optical power such that positive lenses placed in front of the farsighted eye can correct near vision.
In the normal healthy eye, the lens of the eye can accommodate to both near and far distances of the object viewed such that the image of the object is focused on the retina and remains sharp to the patient. For far vision, the ciliary muscles of the eye can relax and adjust the lens to focus on a far object that may be several meters away. For near vision, the ciliary muscles of the eye can constrict and adjust the lens to focus on a near object. The near object can be located at a distance suitable for reading, for example. The eye can accommodate with movement of the lens to focus on objects at intermediate distances.
With age the accommodation of the eye can decrease such that a person with good distance vision may benefit from lenses to see near objects clearly. The decrease of accommodation of the eye corresponding to presbyopia may be related to a stiffer crystalline lens that decreases the accommodative amplitude of the lens of the eye in at least some instances. People who are near sighted and wear glasses for distance vision may find glasses that correct sight for far vision do not provide near vision correction in at least some instance. This loss of accommodation of the eye can be referred to as presbyopia.
Although many forms of optical correction and devices have been proposed to treat presbyopia, at least some of these approaches have one or more deficiencies such that the prior correction of presbyopia may be less than ideal in at least some instances. Although reading glasses can be effective when worn, in at least some instances a person may not have glasses and need near vision. Also, switching from near vision to far vision with reading glasses can be less than ideal in at least some instances. Although bifocals are available, such corrective lenses may provide less than ideal results in at least some instances such as when a person engages in water sport or sweats such that the correction of the lenses can be at least partially distorted.
Although it has been proposed to reduce the stiffness of the natural crystalline lens through laser treatment allowing for improvement in the ability of the crystalline lens to change power, in at least some instances it is possible to create a premature cataract. Also, treatments of the lens can potentially result in changes in refraction that may require the patient to wear glasses in at least some instances. Further, at least some tissue treatments can be unstable in at least some instances such that the treatment results in no more than a temporary change to the eye in at least some instances. For example, electrocautery of the lens capsule may result in decreased thickness of the lens capsule that may contribute to cataract formation and may be related to unstable refraction of the eye in at least some instances.
Patients who receive intraocular lenses (hereinafter “IOLs”) may have no effective accommodation, and may be considered presbyopic in at least some instances. For example, although IOL surgery to replace a cataract of the natural lens of the eye can be effective in restoring vision of the patient, such patients cannot accommodate effectively in at least some instances.
Although multifocal lenses have been proposed, such lenses can result in undesirable visual phenomenon (hereinafter “dysphotopsia”) in at least some instances. Although multifocal lens may provide a first optical correction for near vision and a second optical power for distance vision, the light rays having the second optical power for near vision may provide visual phenomenon such as halos for a distant object, for example when the patient views a distant object.
One promising approach to treat patients who have received IOLs for cataract surgery has been to introduce an accommodating IOL. However, such IOLs have resulted in less accommodation than would be ideal and can be more difficult to implant in at least some instances. Also, recovery time of accommodating IOLs may be longer than a non-accommodating IOL, in at least some instances. Also, the accommodative abilities may not be restored as would be ideal in at least some instances. Though vision may be improved, the degree of improvement can vary among patients and may be less predictable than would be ideal in at least some instances.
In light of the above, it would be desirable to provide improved methods and apparatus for treating vision that overcome one or more of the above mentioned limitations of the prior approaches. Ideally such methods and apparatus would restore accommodation to provide near and far vision correction with reduced side effects.